Many elevators use induction motor drives with inverters, either with U/f-characteristic (voltage or frequency) or vector control. These drives guarantee high riding comfort and short flight times because elevator velocity follows its reference without any significant deviation.
To obtain the advantages of this control method it is necessary to adjust the drive controller according to characteristics of the controlled motor. It is possible but not optimal to run some drives with default values. In many cases, especially with unknown machines, it is better to adjust the controller. This adjustment could be done either manually by "trial and error" or with the help of a motor parameter identification algorithm which measures electrical motor characteristics automatically and then calculates the desired controller values. This identification is done once before the elevator is set into operation the first time and therefore has to operate during standstill. During elevator operation time-invariant parameters are adapted with the help of a motor parameter adaptation algorithm (see copending patent application entitled "Rotor Time Constant Adaptation for Induction Motor in Vector Controlled Elevator Drive" by M. Mann, K. -H. Glahe).
There exist many algorithms to identify motor parameters but they are usually not suitable to elevator drives. Either they operate when the motor is running or they use the motor stator voltage which is normally not measured at elevators (see "Self-Commissioning--A Novel Feature of Modern Inverter-Fed Induction Motor Drives," H. Schierling, Siemens AG, Federal Republic of Germany; and "Selbsteinstellendes and selbstanpassendes Antriebsregelsystem fur die Asynchronmaschine mit Pulswechselrichter," H. Schierling, Dissertation 1987, pages 61-66, Technical University of Darmstadt, Federal Republic of Germany).
While the machine is stationary, only relatively small voltages can be applied. In these cases the pulse-controlled inverter shows large relative errors between the set voltage and the preset desired value. It is conceivable to correct this error during identification if one has an exact knowledge of the frequency converter, but then the procedure would no longer by generally applicable to various frequency converters. Furthermore, that procedure is subject to temperature-dependent and temporal changes.
These preliminary considerations result in the demand for an identification procedure without a knowledge of the motor stator voltage.